612 THE STREPTOCOCCI OF ANIMALS 



small numbers, so that cultivation experiments are necessary to demonstrate 

 its presence. A very highly virulent strain will cause a fatal septicaemia 

 with only slight oedema at the site of inoculation. 



Horses. The disease may also be produced experimentally in the horse. 

 Sub-cutaneous inoculation leads to the formation of an abscess. By rubbing 

 the nasal fossae with a plug of wool soaked in a culture, a clinical condition 

 similar to the spontaneous disease is produced (Schiitz and others). Intra- 

 venous inoculation is followed by an interesting result : it leads merely to a 

 transitory illness but appears to produce immunity (Sand and Jensen). [An 

 abscess forms at the site of inoculation which discharges externally. ] 



Mules, and more particularly asses, are less susceptible to the disease than 

 horses. 



Rabbits are even more highly immune and to produce an infection in these 

 animals the material must be inoculated intra-venously. In that case death 

 takes place from septicaemia. 



Guinea-pigs are almost completely immune though it is possible to set up 

 a fatal infection by inoculating large quantities of a virulent virus into the 

 peritoneal cavity. 



Material for inoculation. For purposes of experimental inoculation a 

 young growth of the first sub-culture in broth, or pus from an abscess should 

 be used. 



SECTION II. MORPHOLOGY. 

 1. Microscopical appearance. 



The micro-organism of strangles is a coccus generally arranged in chains 

 or diplococci, only rarely as isolated cocci ; the chains may be short con- 

 sisting of three or four cocci only, or long and wavy and made up of a large 

 number of cocci. The individual cocci measure 0'7-0'9/x in diameter but 

 oval-shaped cocci with their long axes transverse to the length of the chain 

 are often seen. Encapsulated cocci are not infrequently present in stained 

 films from serum cultures. A distinct capsule has been seen surrounding 

 the cocci in films made with pus from the pleura in a case of strangles 

 (Besson). 



Staining reactions. The streptococcus equi stains easily with the basic 

 aniline dyes Kiihne's blue or carbol-thionin. The organism is gram- 

 positive. Pus from a case of strangles gives very pretty preparations when 

 treated with Gram's stain and counter-stained. 



2. Cultural characteristics. 



Conditions of growth. The streptococcus of strangles is an aerobic and 

 facultative anaerobic organism : it grows best at 37 C. and only poorly 

 below 20 C. According to Schiitz it only grows in broth or on serum ; scanty 

 growths can at times be obtained on agar and gelatin (Nocard, Sand and 

 Jensen). 



Characters of growth. Broth. Glycerin-broth is the best medium. The 

 organism grows like the streptococcus of erysipelas and forms small white 

 flocculi which quickly fall to the bottom of the vessel leaving the medium 

 clear. 



Agar. Cultures have been obtained on sloped agar (Nocard, Sand and 

 Jensen). The growth is more luxuriant if sown in deep stab culture. 



Besson had a strain which grew fairly well on sloped agar for two or three genera- 

 tions ; the colonies were semi-transparent and lenticular-shaped but never exceeded 

 in size that of a pin's head. 



