270 INVERTEBRATE PHYSIOLOGY 



it is to be hoped that some of the very large worms may be adapted to 

 in vivo experiments similar to those with the giant African snail and with 

 Honiarus. 



Secretion 



Any inquiry into physiological processes soon reveals secretion by cells 

 as a common phenomenon to be encountered in the study of almost any 

 organ or system. Investigators very early recognized processes of secre- 

 tion in excretory systems and a vast literature has appeared on the sub- 

 ject. Here we shall confine our attention to recent quantitative studies of 

 secretory processes concerned only with excretion. To facilitate compari- 

 son with the other sections, the same order of treatment will be followed. 



Molluscs 



Martin, Stewart, and Harrison (1954) have applied the method of in- 

 fusion into the blood of the giant African snail, with subsequent serial 

 sampling of blood and urine, to the study of some of the classical com- 

 pounds known to be secreted in other animals. Of their results only 

 illustrative experiments may be cited here. The dye, phenol red, has long 

 been used in such studies and has been concentrated by all the kidneys 

 studied. In the snail kidney, too, this material is taken from the blood and 

 concentrated in the urine. U/B ratios as high as 90 have been observed. 

 Just as in the case of the vertebrates the transport mechanism depends 

 upon an energy source, and the energy supply may be cut off in the snail 

 by treatment with 2-4 dinitrophenol (DNP). After treatment with DNP 

 the ratio falls very nearly to one, and excretion continues at the rate im- 

 posed by the filtration process. 



In cephalopods the application of quantitative methods has a longer 

 history. Mayer and Rathery (1907) made an unnecessarily traumatic, 

 but nevertheless workable, approach to the problem of collecting blood 

 and urine samples from the octopus. Perhaps because they were working 

 wth animals a little too small for really easy sampling, they did not follow 

 blood and urine concentrations at frequent intervals. Under these circum- 

 stances they missed the evidence for filtration and denied its existence, 

 though they described crude experiments which indicated that reabsorption 

 took place. Their evidences for the secretion of glucose, urea, and sodium 

 chloride are not satisfactory because of the failure to correlate the times 

 of sampling blood and urine. Had their work been only a little more re- 

 fined, it might well have set a pattern even for vertebrate studies of the 

 period. 



Somewhat the same criticism can be made of Bruni's (1937) experi- 

 ments. This worker made injections of various dyes intramuscularly in the 



