SECT. 2] AND WEIGHT 517 



even any intimation whether this was based on results obtained by 

 himself or by others. The matter is curious, for 14,000 is, as will 

 be seen, not now regarded as a zone occupied by growth processes. 

 But the equation was first applied in physiology by Snyder, who 

 calculated /x for various temperature/time effects in muscle action, 

 and compared them with others from various sources. Thus he found 

 a /x of 12,800 calories for the experiments of Peter with echinoderm 

 egg-cleavage and of 16,600 for those of Hertwig on amphibian egg- 

 cleavage. He did not, however, carry the question much further, 

 and it was left for Crozier and his collaborators, in a long series of 

 papers, to work out the temperature characteristic for a great number 

 of processes. Before discussing the findings in the case of embryonic 

 growth, we must outline the groups into which Crozier found he 

 could separate living processes as regards their temperature charac- 

 teristic. 



The temperature characteristic of many respiration processes, 

 both in vivo, such as the oxygen consumption of Arbacia eggs, and 

 in vitro, such as the combination of oxygen with haemoglobin, was 

 about 16,600. In many cases an abrupt break in the straight lines 

 would occur; thus below 15° /^ for the oxygen consumption and 

 ciHary activity of mussel gills was 16,000 and above 15° it was 

 11,000, which latter value held at all temperatures tried for the 

 oxygen consumption of the guinea-pig uterus. On the other hand, 

 the rate of progression of all kinds of invertebrates usually had 

 a /A of between 12,000 and 12,500, and such phenomena as 

 the frequency of the firefly flash, the frequency of invertebrate 

 heart beats, and the frequency of noise production also came 

 in this group. A /x of 12,000 would seem to indicate the pre- 

 dominance of a nervous factor, and of 16,000 the predominance of 

 an oxidation. Other processes gave various values of /u,, e.g. 9240 

 for rate of movement of algae, from 4700 to 10,300 for protoplasmic 

 streaming in plant cells, and 7900 for rate of pulsation of infusorial 

 contractile vacuoles. These would possibly indicate the appearance 

 of a physical factor, probably diffusion. Rate of nerve conduction 

 gave 8080 and 10,700. It is probable that even a difference between 

 16,000 and 16,700 is significant, for the former may indicate that the 

 controlling catalyst in the oxidation is iron, while the latter may 

 indicate that a dehydrogenation mechanism is at work; again, the 

 value 11,500, which some oxidations show at some temperatures, is 



