CYTOLOGICAL CHANGES IN THE INFECTED HOST CELL 195 



2. Observations on Fixed and Stained Preparations 



Stained smears, made after the fashion of diagnostic bacte- 

 riology, were the basis of the earlier observations and they were 

 not very informative. More recently, however, cytological 

 methods appropriate for the study of bacteria have been de- 

 vised and these have provided a more rewarding approach to the 

 study of the effects of phage infection on the structure of the host 

 cell. These involve the fixation in situ of the cells in or on the 

 culture medium with cytological fixatives (such as osmium tetr- 

 oxide and other, more complex, solutions) ; the application of 

 selective staining methods allowing the differentiation of the nu- 

 clear chromatin bodies and the cytoplasm, which is strongly 

 basophilic due in large part to RNA (see Murray, Gillen, and 

 Heagy, 1950); and suitable mounting of the preparation to 

 minimize distortion of the cell and to provide for optical needs. 



D'Herelle (1926) described briefly the effects of phage in- 

 fection on the staining properties of the bacterial host. The 

 affinity of the infected bacteria for basic dyes gradually decreased. 

 Weakly staining, amorphous debris gradually increased in 

 amount as the number of intact bacteria decreased. He never 

 saw corroded or broken bacterial cells. The intact cells often 

 became spherical and then burst, becoming amorphous im- 

 mediately. The spherical forms were extremely fragile and were 

 always less numerous in stained specimens than in dark field 

 preparations made at the same time. The phage particles them- 

 selves were below the limits of visibility in the stained prepara- 

 tions. 



Rather similar observations were recorded by Bronfenbrenner 

 (1928). The cytoplasm showed marked changes during the 

 swelling of the bacteria, staining less intensely and more un- 

 evenly so that the bacteria appeared segmented or beaded. In 

 highly swollen bacteria the chromatin was distributed through- 

 out the bacteria in the form of dustlike particles. 



Borrel (1928, 1932) used an iron-tannate-fuchsin mordant 

 which was effective in making visible bacterial flagellae and the 

 larger animal viruses such as vaccinia and moUuscum contagio- 



