SECT. 5] IN ONTOGENESIS 781 



stages, and this was found to be the case by Harrison, who observed 

 that explants of frog spinal cord from 4-5-day embryos would not 

 grow in 0-7 per cent, salt solution (isotonic with adult serum), but 

 would do so perfectly well in 0-4 per cent. Backmann & Sundberg 

 pointed out that this corresponded with a A of — 0-245°, ^^^ ^^ 

 could be explained perfectly on the basis of Fig. 178. 



The work was continued by Backmann, who measured with a 

 micrometer the swelling of frog's eggs in different solutions. Pre- 

 viously some observations on this point had been made by Wilson 

 and by Tonkov, but they were more concerned with the morpho- 

 logical changes caused by salt solutions. This technique afforded a 

 means of checking the measurements already made of the osmotic 

 pressure of the egg-contents, only now Backmann worked with the eggs 

 of Bufo vulgaris and Triton cristatus. In both cases the unfertilised eggs 

 remained without change of diameter for many hours in solutions of 

 A — 0-44°, but the fertilised eggs (morulae) remained without change 

 of diameter in solutions of A — 0-02°. The former eggs placed in the 

 latter solution swelled up by 2-5 per cent, in 48 hours, the latter eggs 

 placed in the former solution shrank by i • 2 per cent, in 24 hours. There 

 was thus every indication that the results previously obtained on the 

 frog held also for the toad and the newt. In these cases also, unfertilised 

 eggs would have a A of — 0-45° and the fertihsed ones — 0-02°. 

 The only difference between the frog on the one hand and the toad 

 and the newt on the other was that, in the former case, there was no 

 perceptible increase of volume after fertihsation, and, in the two 

 latter cases, there was a slight normal increase. 



In 1900 Bataillon had studied the conditions under which the eggs 

 of the lamprey, Petromyzon planeri, would develop. He found that the 

 fertilised eggs of this cyclostome would not develop properly in salt 

 solutions above 0-2 per cent. In 0-5 per cent, the process would 

 not go further than the gastrula stage, in o-6 per cent, only as far 

 as the morula, while in o-8 per cent, no further than the i6-cell 

 stage. From these data Backmann calculated that the osmotic 

 pressure of the egg-interior in the morula stage of Petromyzon must 

 be about A — 0-125°. -^o figures are available for the A of the adult 

 serum of Petromyzon planeri, but Dekhuysen got a value of — 0-49° 

 for Petromyzon fluviatilis, from which it is probably legitimate to con- 

 clude that events proceed in the cyclostome tgg just as in that 

 of amphibia. The only fact still wanting is the osmotic pressure of 



