﻿168 STRONG. 



the previous strain have been described by Kolle and Otto, 25 and exten- 

 sively employed by them in the immunization of various laboratory 

 animals. The cultural peculiarities and morphology of pest "Maassen 

 Alt" are typical of Bacillus pestis and microscopical preparations from its 

 cultures show the characteristic bipolar staining of the bacilli. Such 

 forms are particularly noticeable after the bacillus has been inoculated 

 into the subcutaneous tissues of an animal and several hours later re- 

 claimed in cultures. This organism is also agglutinated by two standard 

 pest sera; it likewise represents a much attenuated strain of Bacillus 

 pestis, although its viridence is not so far reduced as is that of the strain 

 "Pest Avirulent." Guinea pigs of from 200 to 300 grams weight as a 

 rule recover from subcutaneous injections of such large amounts as from 

 one to two agar slant cultures, yet they sometimes succumb to such inoc- 

 ulations. Evidences of a subacute pest infection are visible in the event 

 of their death. In other experiments, when as. much as a whole agar 

 slant culture has been injected intraperitoneal!}', or more rarely subcuta- 

 neously, the animal has died within twenty-four to forty-eight hours, 

 apparently of a toxaunia, the organisms not having multipled to any 

 demonstrable extent, or at least they have certainly not invaded the 

 circulation or the solid organs. This has been demonstrated by the 

 sterility of cultures made from these locations. (See Series 38, animal 

 number 2050, p. 219, and Series 40, animal number 2128, etc., p. 220.) 

 In still other instances in which the guinea pigs have lived six or more clays 

 after inoculation and then succumbed and in which the injection has been 

 made subcutaneously, pest bacilli may be demonstrated in cultures from 

 the buboes which have developed but they may not be encountered in the 

 blood of the heart or any of the other organs of the body. As in the 

 ease of the strain "Pest Avirulent," undoubted proof that the culture 

 "Pest Maassen" represents an attenuated type of Bacillus pestis has been 

 given by the fact that numerous guinea pigs and monkeys have been 

 vaccinated with it and have later -shown high and undoubted immunity 

 against inoculations with the strain "Pest Virulent." (See Series 17, 

 21, etc., pp. 212 to 221.) 



Pest "Avirulent Manila." — The culture "Avirulent Manila" was ob- 

 tained from an autopsy upon a typical case of human bubonic plague 

 occurring in Manila in the autumn of 1903. Its exact viridence at the 

 time of its isolation was not known. It was preserved in the laboratory 

 as a stock laboratory plague culture by Mr. Hare, formerly of this 

 Institute, and was transplanted from time to time on agar. It had not 

 been passed through animals since its isolation up to the time these 

 experiments were begun. In the summer of the year 1905, from 1 to 2 



25 Ztschr. f. Hyg. u. Infectionskrankh., Leipz. (1903), 45, 513. 



