294 ANNUAL REPORT OF THE Off. Doc. 



but the serum does not di-y out as quickly, and the growth of the 

 tubercle bacillus is facilitated. Serum prepared in this manner has 

 been employed throughout for the cultures used in our inoculations. 



Preparation of Cultures for Inoculation^ and Dosage, ■ — The course 

 of an experimental tuberculosis depends so largely on the oumber of 

 bacilli introduced that exact dosage is an important factor in com- 

 parative work. Weighing naturally suggested itself, but a trial 

 soon convinced us of its impracticability. The growth of human 

 cultures is usually so abundant by the second generation, that it is 

 easy to obtain fairly dry masses which can be weighed quite ac- 

 curately, but bovine cultures often grow very scantily for many 

 generations, as a thin film resembling ground glass. We have 

 adopted as a uniform practice the method of Dr. Theobald Smith, the 

 use of a suspension of a given opacitj'. A portion of the g-i-owth is 

 removed to the wall of a dry and sterile test-tube, and rubbed round 

 and round with a glass rod until no lumps can be seen. Bouillon 

 is then added, and after stirring thoroughly, the mixture is allowed 

 to stand quiet for two or three hours, so that the clumps may settle. 

 The upper portion is poured off, and bouillon added until the sus- 

 pension equals in turbidity a. twenty-four-hour-old culture of the 

 typhoid bacillus. The test culture is killed with formalin vapor and 

 sealed, so that it cao be used as a standard for a considerable time. 

 Cover-glass preparations were made always as controls. In the 

 tables below the generation of the cultures is indicated by the ex- 

 ponent, and the age of each culture is given in days in a separate 

 column. For guinea-pigs and rabbits the dose has been through- 

 out 1 c.c. of the suspension, introduced under the skin of the abdo- 

 men. For the other animals the dose and mode of inoculation are 

 given in the tables. 



Morphology and Cultural Characteristics of Bacilli Examined. — 

 The moryihology of the bacilli in cultures of bovine origin is more 

 uniform and constant than in cultures from man. The bovine bacilli 

 are short, seldom more than two w in length, and averaging less. In 

 early generations many are seen which are oval, their length not 

 more than double their breadth. They are thick and straight. 

 They stain with carbol-fuchsin evenly and deeply, and beading is 

 markedly absent, even in old cultures. 



The human bacilli are, as a rule, much longer from the start, and 

 tend to increase in length rapidly in sub-cultures. They are gen- 

 erally more or less curved and some cultures contain many S-shaped 

 forms, as culture M noted above. They stain with carbol-fuchsin 

 less deeply, and beading is a marked characteristic, often seen in the 

 earliest growth. 



These characteristics are most persistent in cultures on blood- 



