MILK IIYGIKM: 115 



suspension may be allowed to settle or filtered through a plug 

 of glass wool, in order to prevent stopping of the needle of the 

 syringe with bits of tissue. 



These precautionary measures must be taken, for the in- 

 jection of large quantities of butter fat into the abdominal 

 cavity of guinea pigs often produces tubercles that are very 

 similar to those produced by the tubercle organism. Inocu- 

 lation of a second animal with such tissue is without effect. 



2. A more rapid method, and one whose delicacy is as great 

 as the intraperitoneal injection of a mixed cream and sedi- 

 ment, is the injection of 1 cc. of the whole milk into the 

 muscles of the thigh of a guinea pig. The enlargement of the 

 lymph glands in the inguinal region is evidence of the pres- 

 ence of tubercle bacilli. The changes often appear as early as 

 the twelfth day after inoculation. For more detailed methods 

 of animal inoculation and post-mortem examination, the stu- 

 dent is referred to standard works on medical bacteriology. 



Exercise. A demonstration of the inoculation and post-mortem 

 examination of an animal should be made by the instructor. 



Examination for pyogenic organisms. The pyogenic or- 

 ganism sought for in milk is Streptococcus pyogenes, since this 

 is the most virulent of all the pus-forming bacteria, and the 

 most frequently found in outbreaks of contagious garget. The 

 examination is of little value, except in the case of perfectly 

 fresh market milk, or in high-grade milk whose bacterial con- 

 tent is largely from the interior of the udeter. The pyogenic 

 organisms do not find favorable conditions for growth in 

 market milk, and are soon crowded out by lactic organisms ; 

 hence in milk of high germ content their detection is difficult. 



The streptococci find most favorable conditions for growth 

 on lactose agar at 37 C. Suspicious colonies on such plates 

 should be inoculated into lactose broth, and this examined 



