XII 

 PATHOLOGICAL HISTOLOGY IN GUINEA-PIGS 



1. DESCRIPTION OF TISSUES 



(a) The central nervous system: In regard to the prolifera- 

 tive lesions of the brain, the vascular lesions, perivascular and 

 meningeal infiltrations are like those in human brains. Stage 

 for stage the processes are identical, and involve the same 

 cells as in the human. The proliferative lesions of the " com- 

 pact" type are perhaps relatively less numerous than in man, 

 while the perivascular grouping of radially directed neuroglia 

 cells, "rosettes" of Spielmeyer and the diffuse proliferation of 

 neuroglia in apposition to capillaries in the molecular layer 

 of the cerebellum and in the superficial layer of the cerebral 

 cortex ("Strauchwerk lesion of Spielmeyer") (page 179) are 

 relatively more numerous. All these types of lesions are to 

 be found in cerebrum, cerebellum, and medulla distributed 

 much as in man. 



These central nervous lesions in guinea-pigs are constant. 

 They may be so numerous as to cause paralysis (Plate XVIII, 

 figs. 45 and 46) and death or so few as to require sections from 

 several parts of the brain for their detection. Otto and Diet- 

 rich (1918) were the first to describe them in the guinea-pig 

 and to indicate that they could be recognized in frozen sec- 

 tions. We have found these lesions in the brains of thirty-six 

 guinea-pigs in a consecutive series; and unhesitatingly take 

 the position that their presence is an indispensable criterion 

 for the proof of typhus in the guinea-pig. In guinea-pigs 

 killed in the first forty-eight hours of temperature, only vascu- 

 lar lesions may be present, although we have had but one such 

 instance. For the early diagnosis, i.e., before the third day of 

 temperature, we recommend paraffin sections, for later periods 

 frozen sections stained with methylene blue suffice for the 

 recognition of the compact lesions. 



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