138 RICKETTSIA PROWAZEKI IN LICE 



infection commences with the rod-shaped rickettsia or with 

 some other form possibly the minute paired granules which 

 have been observed in swollen cells of lice, certainly exposed 

 to infection, in which definite rickettsia are not found (Box 

 LII). The bacilliform stage when present in large numbers 

 (Fig. 30, plate IX) distend the cell and the rod elements seem 

 to grow in chains which are parallelly arranged in coils within 

 the cell. When present in small numbers the cells containing 

 them remain normal in appearance and only careful study 

 with the oil immersion objective will reveal them, often in 

 short chains irregularly arranged in various directions in the 

 cytoplasm of the cell (Fig. 28, plate IX). Occasionally but 

 one or a few rods are found in a cell, and these seem to be sur- 

 rounded by a halo or unstained area. 



In practically all lice containing the minute coccoid forms, 

 the rod forms have been seen (Fig. 33, plate X). 



The forms seen free in the lumen of the gut have been the 

 small coccoid and pair forms, singly or in chains, and the thread 

 or filamentous forms. The latter sometimes seem to gain en- 

 trance independently of rupture of the epithelial cells while 

 the former probably only gain entrance into the lumen when 

 the over-distended cells containing them rupture. 



We have never been able to find rickettsia in any organ of 

 the louse other than the alimentary tract. Our material sug- 

 gests that the infection begins in the anterior part of the mid 

 gut, probably in or near the diverticulae, and that the thread- 

 like and bacillary forms precede the appearance of the small 

 coccoid and streptococcoid forms. 



We could not confirm Sikora's (1920) finding of rickettsia 

 in the salivary glands. It is easy to exclude their presence 

 from the tubular salivary glands. The reniform salivary gland 

 cells are so filled with secretory granules that recognition of 

 micro-organisms as minute as rickettsia is a matter of doubt. 

 Comparison of salivary glands in sections of infected and con- 

 trol lice shows no differences and we believe that this organ does 

 not become infected and that it cannot be a usual site of mul- 

 tiplication of Rickettsia prowazeki. 



