664 ACTIVE IMMUNIZATION 



in consequence of which every inoculation will produce a reaction that 

 may be injurious to the patient. 



Preparation of Tuberculins. The knowledge that tubercle bacilli 

 and their secretions as seen in vitro contain both desirable and undesir- 

 able substances has led Koch and others to adopt different methods of 

 preparing tuberculin in the endeavor to obtain the desirable immunizing 

 principles in as pure a state as possible. 



As a consequence, a large number of preparations have been advo- 

 cated from time to time, all of which are said to possess some special 

 properties and virtues. All tuberculins, whatever their mode of pre- 

 paration and manufacture, are derived from cultures of the tubercle 

 bacillus. So numerous have the tuberculins become, and so superior 

 are the advantages claimed for each new product over the older ones, 

 both for diagnostic and for therapeutic purposes, that only a few of 

 those possessing special interest and value can here be described. 



1. Old Tuberculin (0. T.). This is Koch's original tuberculin, and 

 is the variety regarded by many as the most useful both in diagnosis 

 and in treatment. Its manufacture was based upon the principle that 

 the toxins elaborated by the bacilli into the culture-medium or liberated 

 by disintegration of the bodies were chiefly concerned in stimulating 

 body-cells to the formation of antibodies. Since the bacillary bodies 

 were regarded as mainly responsible for the production of abscesses at 

 the point of inoculation, they are eliminated by a process of filtra- 

 tion. 



Old tuberculin is prepared as follows: Large shallow flasks contain- 

 ing 5 per cent, of glycerin alkaline broth are inoculated with a culture 

 of human tubercle bacilli and grown at body temperature for from six to 

 eight weeks, at the end of which time the bacilli have grown into a flat 

 sheet covering the surface of the fluid (Fig. 133). The entire contents 

 are then subjected to a current of steam over a water-bath for the pur- 

 poses of sterilization and for concentration into one-tenth of the original 

 volume. The glycerin, which is not evaporated, thus constitutes 50 

 per cent, of the resulting mixture. The bacilli are removed by filtration 

 through a Berkefeld or Chamberland filter. The filtrate is a clear, 

 brown fluid, of a characteristic odor, which keeps indefinitely and is 

 ready for use. 



Koch considered the soluble toxins of the bacillus as the desirable 

 immunizing agents, and believed that the endotoxins were responsible 

 for the necrotic effects. Since, however, it was accepted that bacter- 

 iolytic substances would be formed only after the injection of intact or 



