CPIAPTER V 



THE 1?ETTCUL0-END0THELTAT. SYSTEAF 



It is interest iiio" to note tliat; the concepts we now hold as to 

 celhilar immunity liave their roots buried deeply in experimental 

 biology, chemistry, and pathology. It was the zoologist, Metch- 

 nikotf, who about 1883-84 extended the then existing knowledge of 

 the distribution and functions of amoeboid cells throughout the 

 body and classified them into two groups which he named mac- 

 roplmges and micvoplwges, respectively. He grouped together the 

 fixed phagocytes which he found in the liver, spleen, lymph nodes, 

 and in the central nervous system and the large free mononuclear 

 phagocytic cells of the circulating blood and named them mac- 

 rophages, while the neutrophilic leucocytes of the blood he called 

 microplwges. 



It was his opinion that the macrophages were concerned with the 

 phagocytosis and digestion of dead and foreign animal cells and 

 debris while the function of the microphages was to engulf and de- 

 stroy bacteria. The cellular enzymes which carried out the diges- 

 tion of the phagocytized material he named macrocytase and 

 microcytase, respectively, to indicate the type of phagocyte which 

 produced them. These enzymes have been studied rather ex- 

 tensively by Opie (1906-1910). He found that the macrophages 

 contain an enzyme that resembles pepsin in that it acts best in an 

 acid medium while the microphages contain a trypsin-like enzyme 

 that works best in an alkaline medium. 



Before Metchnikoff began his work on phagocytosis, a great deal 

 had been learned about the manufacture of dyes and their use in 

 histology. According to Conn (1933) it is well established that 

 Hill employed carmine in his histological studies of plant tissues as 

 early as 1770 and there are claims made that either Sarrabat (1733) 

 or E^ichel (1758) were the first to use stains in histological work. 

 About 1854 William Perkin prepared, for the first time, an anilin 

 dye. The discovery of various other dyes now used in biology 

 quickly followed. 



According to Jaffe (1938), it was Ehrlich's (1879) studies on 

 the chemical constitution and cellular affinity of dyes that were re- 



87 



