Especially noteworthy, and strongly indicative of the danger arising from the use of feed containing butyric acid bacilli, is the condition that the cheese maker has no means of detecting the noxious bacilli in fresh milk. While the technician, by the fermentation test, can easily recognize the presence of undesirable gas-forming organisms of the group B. coli, the spores of the butyric acid bacilli do not reveal themselves so readily. They do not germinate in milk at 30° to 40° C., and milk samples containing thousands of these harmful organisms can be apparently satisfactory when judged by ordinary examination. Thus, during the manufacture of cheese made from this questionable "silage milk" the danger can not be observed at first, and not until after several weeks, when the cheese is in the fermenting room, do these unfavorable tendencies begin to appear. The nonproduction of butyric acid bacilli spores in milk is one of the peculiarities especially characteristic of this bacillus, as is also the fact that the presence of these undesirable bacilli is in no wise disturbingly noticeable in the preparation of cheese made from skimmed milk. That just the highly heated Emmental cheese affords an excellent growth for the motile butyric acid bacilli is obviously correlated to the acid condition, which is in this type of cheese most favorable for the bacilli, and to other conditions which are still undetermined.

IV. THE TRANSMISSION OF MICROORGANISMS FROM THE FODDER INTO THE MILK.

The germination in milk of organisms originating in the feed can be accounted for in many ways. In the first place, if we consider that the people who care for the feeding usually look after the milking too, and that with bacteria on their hands after handling the feed they milk the cows and attend to the milk utensils, it is evident that it is only a short step to the actual infection of the milk. It is also possible that particles of the food are conveyed to the milk through the manipulations of the attendants. A dispersion of harmful microorganisms by air currents is barely possible in the case of moist silage.

Our investigations have led us to conclude that the most feasible mode of transferring the infection is through the alimentary canal of the cow-that is, the harmful butyric acid bacilli from the ensilage are conveyed into the milk from the feces of the cow. As one might conclude, the butyric bacilli are in the form of spores at the time the fodder is used. These are not destroyed by the juices of the digestive system and are excreted with the undigested particles of the fodder in a form capable of regerminating. A germination of spores and an increase in the numbers of bacilli do not seem to occur in the body of the animal. Relative to this it may be said that the butyric acid bacilli count in the feces rises and falls in accordance to the increase or decrease in the butyric acid bacilli content of the feed.

Now one could not say that the transmission of bacteria from the manure into the milk would be possible only with gross neglect in the sanitary handling of the milk during milking. This transportation is accomplished largely by indirect processes. The usual contamination of milk is explained by the fact that manure frequently

gets on the flanks and udders of the cows, dries there, and can not be removed by the helpers. Then, too, some dried manure can be blown as dust around the stable and each small particle may carry any number of bacteria. It is not necessary to explain the possibility of infecting the milk during milking by the unavoidable shaking off of dirt particles from the cow's body, if we consider that the count for butyric acid bacilli spores is millions per gram, and therefore thousands per milligram, and that the fractional part of a milligram can effectively inoculate the quantity of milk used in an ordinary Emmental cheese.

V. ON THE QUESTION OF THE RELATION OF THE SO-CALLED STINKERS TO EMMENTAL CHEESE SPOILED BY BUTYRIC ACID FERMENTATION.

As was previously mentioned, the butyric acid bacilli usually enter the milk and cheese in the form of spores. The very presence of the spores in the cheese mass would not be detectable were it not for the development of the spores into bacilli in the cheese, with their consequent increase and the formation of the characteristic byproducts, gas and butyric acid. Other organisms also enter into the milk and would be equally harmful, were they able to sustain themselves. The hay and potato bacilli, for example, could dissolve the cheese and change it to a slimy mass. Fortunately, these organisms do not find favorable conditions in the cheese, and for this reason it makes no difference if there are larger or lesser numbers of spores of the kinds in question in the cheese milk.

Similar experiences are had, at least in Switzerland, with B. putrificus. This organism possesses a very dangerous characteristic, inasmuch as it can, with complete exclusion of air, dissolve the casein and thus separate out the strong-smelling and strong-tasting byproducts of metabolism. The spores of these bacilli are widely spread in nature; and inasmuch as they are contained in the feces of domestic animals, it is not surprising to find them in milk and cheese. In our own experiments with Emmental cheese they were found regularly, but in small numbers. It is important and fortunate that they are not able to grow and reproduce except under especially favorable conditions. Now and then, but only seldom, certain cheeses from a creamery show defects, namely, parts of the inside appear white and crumbly, with large irregular holes, and have a bad taste and smell which permeate the good parts. The bacteriological examination of such cheese, as a rule, shows the presence of spore-forming B. putrificus and such cases were at once called putrificus cheese. Under what conditions the usually harmless putrificus bacilli ferment in the cheese and cause bad results is yet to be determined.

With the discussion of the characteristics of putrificus cheese we are reminded of the "stinkers," which are a source of considerable loss for American cheese makers. The putrificus cheese also is really a stinker, and the analogy of both types of defective cheese is easily understood when one remembers that the specific flavor and smell of stinkers are largely due to B. putrificus. We have discovered thousands of spores from that bacillus in a single gram of stinker cheese which we have had occasion to examine and, in addi

tion, hundreds of thousands of butyric acid bacilli spores. In this respect, that is to say, the high content in butyric acid bacilli, the American stinker differs from our Swiss putrificus cheese. So, from a bacteriological standpoint, the defective type stinker might be a combination of defective types of putrificus and butyric acid bacilli

cheese.

With reference to this circumstance one can not put aside the reflection in regard to the origin of the stinkers, that with the latter as well as with butyric acid bacilli cheese, an infection of the milk and consequently of the cheese, with large quantities of butyric acid bacilli, plays the chief rôle, and this evil can be controlled only by avoiding the source of infection. In Switzerland it is well known that the source of infection lies in the use of unsuitable silage, and the same might be the case in America. This suspicion has also been expressed among American Swiss cheese makers who believe the widespread use of silos to be responsible for the numerous defective products, especially stinkers. However, modern scientific practice may well recommend the use of corn for silage, as it would not have been possible by any other manner to bring the agricultural and dairying industries in the United States up to their present high stage of development. Therefore the use of silage must not be reduced, but the technical side of silage preparation ought to be developed to the highest efficiency so that it will be possible to determine a practical control for the dangers of infection, which result from the use of milk affected by harmful biological agencies acting through the silage. With all due care in the handling and preparation of the silage there are still factors which play their part in determining the quality of the silage, and which can not be controlled except by more or less appropriate adaptation to their presence. On these grounds the opinion is justified, that the American corn silo affords that method of preservation which allows a pure lactic acid fermentation to come up in the fodder, with exclusion of the fermentation of harmful allied organisms; although for other reasons the quality of this ensilage is sometimes inferior, at least with respect to the production of milk for Emmental cheese. The numerous defective products found in American cheese factories as the result of butyric acid bacilli and other spore-forming organisms might be explained for the present by the use of unsuitable ensilage in certain dairy farms.

Chairman SAMMIS. I am sure Doctor Burri will be pleased to answer any questions you might have.

Dr. G. L. A. RUEHLE (Michigan Agricultural College). I should like to ask how the sweet silage you spoke of is made?

Doctor BURRI. It is made in the following manner: Layers of grasses are cut and half dried and piled on layers so you have a very, very quick rise in temperature. Temperatures are raised to 45° to 50° C. in a very short time. When the weather is beautiful you can put in a layer of about 6 feet, so you have at least a mass or package at a temperature of 45° or 50°. This temperature is strong enough to destroy lactic acid forming bacteria and give better condition for

the spore.

Doctor RUEHLE. Is that soon after it is made or is it kept for a considerable time? I mean how long after it is prepared is it suitable for feeding to the animal?

Doctor BURRI. Usually they begin feeding it in December. Sometimes the grasses are cut in May and June, or about the time they are making hay.

Chairman SAMMIS. Doctor Burri, isn't this silage pressed under a screw so as to press it together tightly and exclude the air?

Doctor BURRI. Yes; it is made under pressure, but only after it has been finished. The pressure is a means to keep the temperature at a certain height.

Chairman SAMMIS. The tighter you press it, the cooler it stays, is that it?

Doctor BURRI. Yes. This kind of silage was used about 1830, I believe. The process is called from a Frenchman, but I believe it came from America.

Doctor RUEHLE. How do you explain the entrance of the bacteria into the milk.

Doctor BURRI. By manure.

Chairman SAMMIS. Doctor Burri, with reference to the third slide from the end in which you showed a large bloated cheese broken apart. I remember seeing such cheese at the factory. They produced such cheese right along for a time and we thought it was due to yeast at that time, because the first day when we steamed the whey the trouble stopped, so it did not seem to be due to anything which had spores in it. I presume in many cases the germ produced this.

Doctor BURRI. After our experiments we came to the conclusion that yeast can not spoil a cheese in this manner. Very seldom do we have this effect with the yeast.

Chairman SAMMIS. Are there any further questions? Gentlemen, the next subject on our program, and we shall have to move along rapidly, is "The use of bacterial cultures for controlling the fermentation in Emmental cheese" by Dr. J. M. Sherman, bacteriologist, United States Department of Agriculture.

THE USE OF BACTERIAL CULTURES FOR CONTROLLING THE FERMENTATION IN EMMENTAL CHEESE.

JAMES MORGAN SHERMAN, Ph. D., research laboratories, Dairy Division, United States Department of Agriculture.

It is the purpose of this paper to deal with the progress which has been made by the United States Department of Agriculture in the improvement of our domestic cheese of the Emmental type by the use of bacterial cultures. The developments which have taken place in this work in America are not so much the discovery of the types of bacteria in Emmental cheese (that was done by von Freudenreich and his various coworkers many years ago) as their application in the industry.

THE CONTROL OF THE INITIAL FERMENTATION.

In order that the proper fermentation of the lactose may be initiated, and undesirable fermentations, especially gassy fermentations, suppressed, Doane and Eldridge used a culture of Lactobacillus bul

garicus. 8his organism, which is closely related to the B. casei of von Freudenreich (Thermobacterium helveticum, Orla-Jensen), has now been used in this country for a number of years with marked

success.

Contrary to the experience of some of the European workers with the helveticum type, the Lactobacillus bulgaricus which we have used does not appear to contribute directly to the flavor of the cheese, though indirectly, through the suppression of undesirable bacteria, a general improvement in quality is effected.

In factory practice this culture can be propagated in bulk without difficulty in either whey or skimmed milk. On the whole, we have found milk more desirable for this purpose, as a convenient practical check can be maintained on the purity and condition of the starter by an examination of the nature of the curd formed. An incubation period of 18 hours at a temperature of about 45° C. has given very satisfactory results under factory conditions. Although Lactobacil lus bulgaricus makes a rapid growth at lower temperatures than 45° C., it has been found that the troubles from contamination, under the practical conditions obtaining in the factory, are reduced when the higher temperature of incubation is used. While the amount of the bulgaricus starter which may be used in the manufacture of Swiss cheese can be varied considerably without apparent effect upon the finished product, the rule which has been followed in this country is to use a quantity equal to 0.5 per cent of the volume of milk employed.

THE PRODUCTION OF EYES AND FLAVOR.

Although it was over 15 years ago that von Freudenreich and OrlaJensen isolated propionic acid-producing bacteria from Emmental cheese, practically nothing was done during the decade following their discovery toward the practical utilization of these organisms in the manufacture of cheese. In America, the domestic cheese of the Emmental type is usually lacking in the characteristic sweetish flavor, and is frequently either deficient or abnormal in eye forma

tion.

To overcome these defects we have used a variety of the propionic acid-producing bacteria, Bacterium acidi-propionici which insures the development of the characteristic flavor as well as the formation, of eyes. Five years' experience with this culture in both laboratory and factory experiments has convinced us that it is the most essential of any single organism to the production of the desirable characteristics of Emmental cheese. Although it appears to be able, almost by itself, to produce the desirable qualities of Emmental cheese, it apparently plays little, if any, part in the suppression of the undesirable organisms which so frequently injure the quality of the cheese.

While large cheese companies which maintain laboratories can grow the propionic organism for their own use, this procedure does not seem practicable for the small factories. We have, therefore, grown this culture in central laboratories so that it can be supplied in convenient sized bottles to the smaller factories. Grown in a medium consisting of 2 per cent pepton and 0.3 per cent lactose, this culture may be held for at least two weeks at ordinary factory