BUEEAU OF ANIMAL INDUSTRY. 33 



in 57 similar experiments made by competent investigators in this and 

 foreign countries. This experiment lasted ninety days and included 

 the milk of 5*J tuberculous cows. A synojjsis of the results shows that 

 one or more of the guinea pigs fed with milk from different cows 

 have succumbed with tj^pical tuberculosis; that is. the milk of 16.1 

 per cent of the 56 reacting cows has been found to be jjathogenic to 

 guinea pigs when fed to them. Of the experiment animals inoculated 

 intraabdominally, in the first series at least, one guinea pig has died of 

 tuberculosis in each of six different instances, showing that the milk 

 of 10. 7 per cent of the 56 reacting cows in this experiment has proved 

 fatal to guinea pigs in the first inoculation experiment. In the sec- 

 ond series of intraabdominal injections the milk from 7 indi^'idual 

 cows out of 4:5 examined, or 15.5 per cent, was demonstrated to possess 

 virulent tubercle bacilli. By uniting these inoculation results it will 

 be observed that 11 out of 56 cows, or 19.6 per cent, secreted milk 

 which transmitted tuberculosis to one or more experiment animals 

 when injected into the peritoneal caA^tj'. 



Owing to the gi'eater percentage of positive results obtained from 

 the second inoculation experiment, conducted more than two months 

 after the first intraabdominal test, it appears probable, as would be 

 expected, that the virulence of the milk increased wilh the advance- 

 ment of the disease in the cow. The lack of uniformity of results 

 obtained in many of the cows might be explained f i-om our knowledge 

 that tubercle bacilli are not excreted by the normal udder with any 

 degree of constancy. For this reason the continuous feeding experi- 

 ment, coxering a period of three months, seems to have more prac- 

 tical value in demonstrating the transmission of tuberculosis than the 

 inoculation test, where the only possibility of affirmative results must 

 depend on the contingency of the accidental excretion of the bacilli 

 on one particular day. 



The combined results of the ingestion and inoculation experiments 

 show that the milk of 12 out of 56 reacting cows, or 21.4 per cent, has 

 at one time or another since the beginning of the experiment con- 

 tained virulent tubercle bacilli. 



Cover-glass preparations of the centrifugalized sediment of milk 

 from 4 out of 55 cows, or 7.3 per cent, revealed the presence of the 

 tubercle bacillus, and in two of these cases the centrifugalized cream 

 was also found to possess this organism. In one case (cow ISTo. 10) 

 tubercle bacilli were only demonstrated by microscopic examination 

 of the centrifugalized sediment. The number observed were very 

 few, 3 in one slide and but 1 in another, while the remaining 9 

 cover-glasses were apparently free from this bacillus. It appears 

 singular that positive results were not obtained by the intraabdominal 

 injection of this sediment from which the cover-glasses showing the 

 tubercle bacilli were made. Wj^ssokowitsch, in his experiments 

 regarding the quantity' of bacilli requisite for the jiroduction of tuber- 

 culosis by injection into the peritoneal cavity, found that it required 

 at least oO bacilli for the transmission of the disease. Granting this 

 conclusion, it is evident that the milk injected either did not contain 

 a sufficient number of bacilli to cause the disease or that the bacilli 

 were less vigorous or the guinea pigs more resistant than in the other 

 experiments. It is also of interest to know that of the guinea pigs 

 that succumbed to tuberculosis as a result of intraabdominal inocu- 

 lations, 7 were injected wdth a mixture of milk and cream, 5 with 



AGR 1902 3 



