494 THE TUBERCLE BACILLUS GROUP 
Active immunization has been attempted with the following types 
of preparation: 
1. Tuberculins. 
2. Vaccines. 
(a) Killed cultures. 
(6) Soluble vaccines. 
3. Living tubercle bacilli. 
(a) Virulent organisms, Webb method. 
ih) Attenuated viruses. 
(c) Alien acid-fast bacilli. 
4. Sera. 
It has long been recognized that various tuberculins do not confer 
immunity upon experimental animals, although in skilled hands they 
possess undoubted curative value. ^ Killed cultures of tubercle bacilli 
have not been satisfactory, and their use has been greatly restricted 
by the non-solubility of the organisms which produce local indurations 
of refractory nature. Soluble vaccines including "bacillus emulsions" 
and various proteins of the bacillus do not appear to confer definite 
immunity upon susceptible animals. The superiority of living viruses 
over the various preparations of killed organisms and their products 
for protective inoculation is conceded by the great majority of inves- 
tigators. Webb and Williams- have attempted to induce artificial 
active immunity in experimental animals by injecting virulent tubercle 
bacilli, beginning with one or two organisms and gradually increasing 
the number. Their results, while few in number, appear to be worthy 
of serious consideration. The use of attenuated cultures and of alien 
acid-fast bacilli have not been generally regarded as successful up to the 
present time.-^ Sera have been equally unsatisfactory. 
Bovine Tubercle Bacillus. — Cattle and swine are susceptible to 
infection with the bovine tubercle bacillus and the disease is widespread 
among dairy herds. Statistics indicate that in certain parts of the 
United States the incidence of tuberculosis in swine increases almost 
proportionately to the spread of the disease among cattle. This 
condition is brought about partly through the practice of feeding 
slaughter-house of^'al to swine, chiefly through dairies and cheese 
factories where the skimmed milk or whey forms a not inconsiderable 
part of the rations of swine. Scrofula or tuberculosis of swine thus is 
a true ingestion disease. It is possible to infect swine by feeding human 
tubercle bacilli; the spontaneous disease, however, is almost invariably 
an infection with the bovine type of the tubercle bacillus.* 
The most common initial lesion in cattle is an involvement of the 
retropharyngeal glands; the lungs are frequently infected, and occa- 
sionally the liver and serous membranes are invaded rather early in 
' Trudeau: Osier's Modern Medicine, 192.5, vol. 1, Chapter VI. 
2 Jour. Med. Res., 1909, 20, 1; 1911, 24, 1. 
' For excellent discussion see Long (Jour. Prev. Med., 1926, 1, 31. 
* Theobald Smith: Boston Med. and Surg. Jour., 1909, 159, 707. 
