ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 465 



Hud it is not eas) to determine their systematic position unless they are 

 sufficiently advanced towards the structure of the adult fish. In all 

 cases assistance is afforded by the number of myotomes and of fin-rays, 

 if these be developed. 



Pood of Small Shore Fresh-water Fishes.* — A. S. Pearse has 

 studied this in the lakes, swamps, and streams near Madison, Wisconsin. 

 Of the sixteen species examined, nine (viz. basses, sunfish, darters, 

 miller's thumb, and silversides) obtained their living largely from 

 insects or thei^- larvae. Among the other seven species, two had the 

 major part of their food from Ostracods, two from Copepods, one from 

 Cladocera. Thus Entomostraca form the main food of six species. 

 The remaining two {Notropis heterodon and N. cayuga) showed mud 

 and detritus ; nine of the species are too small to be used by man. but 

 they are probably of some importance as food for larger forms and in 

 other ways. The seven species used by man depend mainly on insects, 

 insect larv^, and Entomostraca. It is noted by Forbes that the very 

 young perch feeds on Entomostraca and minute Dipterous larvte ; after 

 it is 1^ in. long it depends more on insects ; as an adult it devours 

 molluscs, crayfishes, and fishes. 



Transfusion of "Kept" Red Blood Corpuscles. f — Peyton Rous 

 and J. R. Turner have succeeded in keeping erythrocytes of the rabbit 

 for a fortnight in mixtures of blood, sodium citrate, saccharose and 

 water. Transfusion experiments were carried out by which a large part 

 of the blood of a rabbit was replaced by " kept " blood. The erythrocytes 

 preserved in vitro and reintroduced remained in circulation and function 

 so well that the animal showed no disturbance. Cells kept for longer 

 periods, though intact and apparently unchanged when transfused, soon 

 leave the circulation. They are disposed of without harm. Perhaps 

 " kept " human cells could be similarly used to replace lost blood. 



Protection of Pathogenic Micro-organisms by Living Tissue 

 Cells.J — Peyton Rous and F. S. Jones have made experiments, e.g. 

 with Bacillus typhosus and the leucocytes of the guinea-pig, which go 

 to show that living phagocytes are able to protect ingested organisms 

 from the action of destructive substances in the surrounding fluid, and 

 even from a strong homologous anti-serum. There is evidence that the 

 protection by phagocytes is largely, if not entirely, dependent on their 

 being alive. It remains to be determined how far the protection of 

 micro-organisms by living tissue cells, especially cells incapable of 

 killing the micro-organisms, is important in disease processes. An 

 infective agent may be walled off from the action of body-fluids and 

 kept alive for a long time. 



* Bull. Wisconsin Nat. Hist. Soc, xiii. (1915) pp. 7-22. 

 t Journ. Exper. Med., xxiii. (1916) pp. 219-37 and 241-8. 

 t Journ. Exper. Med., xxiii. (1916) pp. 601-12 (1 pi.). 



