SCIENCE. 



55 



cular plate is a spiral groove info which works a pin 

 controlling the stage. Mr. Griffith states that with this 

 appliance, a very perfect focal adjustment can be ob- 

 tained. 



Illustration No. i shows the instrument attached to a 

 table by a screw support, the mirror placed in position 

 above the stage. As an adjunct to a dissecting table the 

 Griffith microscope, thus used, would be found most 



useful, occupying no surface space. In excursions it 

 could by the same means be attached to the side of a 

 tree or to a ferce. No arrangements have been as yet 

 completed for the manufacture of this instiument, but it 

 is believed they will shortly be made by a firm who will 

 undertake to produce them at a reasonable cost, as 

 Mr. Griffith has aimed to construct a serviceable portable 

 instrument at a moderate price. 



Griffith's Portable Microscope. (Fig. 2.) 



ON CHICKEN CHOLERA : STUDY OF THE CON- 

 DITIONS OF NON-RECIDIVATION AND OF 

 SOME OTHER CHARACTERISTICS OF THIS 

 DISEASE * 



By M. L. Pasteur. 

 I. 



In the communication which I had the honor of pre- 

 senting to the Academy in the month of February last, I 

 announced, among other results, that chicken cholera 

 originates in a microscopical parasite ; that there is an at- 

 tenuated virus of this disease, and that one or more inocu- 

 lations of this attenuated virus may preserve chickens from 

 death when inoculated with the virus of maximum viru- 

 lence. On account of the striking similarity that these two 

 forms of virus present with the effects of variola and vac- 



i^T r ^ Iat ^ fr ° m the C Z'"% e U Rend » s <t* l' Academic de Sciences, of 

 April 26th 1880, page 952, by P. Casamajur. The translation of the first 



d er 8°8 1 ) SerlCS appeared ln the Chemical News, vol. xli., page 4 (July 



cine in man, it becomes interesting to ascertain not only 

 if the immunity from the more aggravated form of virus 

 is absolute, for the regions of the body which have under- 

 gone the preventative inoculation, but also if this immu- 

 nity exists in the system, no matter what portion of the 

 animal may have been inoculated, and what may have 

 been the manner of introducing the virus.f 



To explain with brevity the results which I have to com- 

 municate, I may be allowed to use the word vaccinate, to 

 express the act of inoculatinga chicken with the attenuated 

 virus. This being admitted, I may state, as the result of 

 many experiments, that the effects of vaccination are very 

 variable. Some chickens are little affected by the most 

 virulent virus after one inoculation of the attenuated virus ; 

 others require two such inoculations, and even three. In 

 every case, the preventive inoculation does some good, be- 



t From all I have seen and read of vaccine in man, and from my experi- 

 ments on chicken cholera, I infer that vaccine rarely acts as a complete 

 preventative. There are cases cited of vaccinated persons who have had 

 the variola, and there are even cases of persons who have had it, after- 

 wards, as much as three times. 



