384 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



THE EXPERIMENT STATION. 



The general character of the work at the bureau's Experiment Sta- 

 tion at Bethesda, Md., has been similar during the last fiscal year to 

 that of former years, consisting of independent investigations and 

 investigations in cooperation with other divisions of the bureau wit!i 

 relation to diseases of animals, and the provision of facilities for the 

 other divisions to make investigations of a kind that require farm 

 and field conditions not obtainable within the limits of the city, and 

 the use of large animals which can not well be kept in the city. 



INFECTIOUS AHOKTTON. 



Among the independent investigations, if valued by the results 

 obtained, the most important and interesting is that which deals with 

 the bacillus of infectious abortion of cattle. 



In the last annual report, and again in a paper written somewhat 

 later, attention was called to a bacillus, slowly and insidiously patho- 

 genic for guinea pigs, found to occur with a fairly highly degree of 

 frequency in cow's milk. The bacillus was defined as a seemingly 

 undescribed organism which probably had escaped detection because 

 of the difficulties associated with its artificial cultivation and the 

 length of time it requires to cause well-marked lesions in experiment 

 animals inoculated with it. and which merited careful study by those 

 who are interested in the widespread movement for the purification 

 and improvement of the commercial milk supply, especially as its 

 presence in milk had been traced directly to the udders of apparently 

 healthy cows. This bacillus, in the course of the year, was definitely 

 proved, both by the experiment station and b.y the Pathological Di- 

 vision to be the germ of infectious abortion of cattle, which had not 

 previously been demonstrated to occur in milk. 



What light this discovery will throw on the subject of infectious 

 abortion generally it is too early to predict. At present it is inter- 

 esting to note that we have found that cows may continue to expel the 

 abortion bacillus with their milk continuously for several years with- 

 out giving evidence of their infected condition by aborting or in any 

 other known manner. In this respect apparently healthy cows may 

 present all the phenomena and represent all the dangers of unsus- 

 pected carriers and dispensers of disease germs. 



The studies we have made on the occurrence of the abortion bacillus 

 in ordinary market milk indicate that infectious abortion is a com- 

 moner disease in dairy herds than we formerly believed it to be, that 

 its frequency is increasing, and that vigorous measures should be 

 taken against its further spread. 



"Whether the abortion bacillus has the power to injure human health 

 remains unknown, although some work with this question in mind 

 has been done at the station. The observation has repeatedly been 

 made that the injection of guinea pigs with cultures of the bacillus 

 mixed with cultures of some other ordinarily harmless bacteria causes 

 pathological conditions that are unlike those caused by the injection 

 of pure cultures alone, and that the difference in the lesions found 

 in the guinea pigs injected respectively with pure and with mixed 

 cultures is in many respects similar to the difference observed in the 

 lesions caused by the injection of pure cultures of the abortion 



