48 



makes the analysis of this problem especially hard. In a special 

 chapter I wiU discuss briefly the importance of this development 

 of acidity in dying tissues ; for the present I will confine myself 

 to a report on analogous experiments on Arbacia andThyone. 



Experiments of the same kind as the ones described above, 

 have been made on the guts of these two species. The guts 

 were crushed with sand, taken up in some water and added 

 with toluene, olive oil and some water. 



In the case of Arbacia 8.5 gr. gut was used — wet weight — . 

 After two weeks the etheric extract of the material appeared to 

 need 11.34 c.c. of twentieth normal KOH for its neutralisation 

 whereas a control sample of the same amount of olive oil 

 only required 1.80 c.c. 



The same thing proved to be true for the cucumber. The 

 amount of gut used here was 19 gr. — wet weight and including 

 the ..calcareous ring" — . After l'/2 week this digest required 

 16.3 c.c. of 0.05 N KOH for neutralisation, while for a control 

 8.0 c.c. were needed. 



Whereas this series of experiments gave rather undefinite 

 evidence, there are others which have given me the absolute 

 proof that a digestion of fats takes place in Echinoderms. 

 Starfishes and sea-urchins were fed on olive oil. The methodo- 

 logy of such experiments will be described in chapter 20 and 

 21 ; it is rather difficult to inject a syrupy fluid like olive oil, 

 but after some practice one easily succeeds in forcing the animals 

 to take it. 



At different intervals the animals were dissected and their 

 guts taken out. They were fixated in F lemming's fluid. The 

 usual imbedding proceedure in paraffin could not be used be- 

 cause I wished to avoid the passing through the alcohols, which 

 might dissolve out the fats. For this reason I used a very old 

 method, recently very much improved by Mc. Junkin 72*). 



This method is based on the principle of imbedding the 

 material in soap. This can take place by passing the material 

 right away from water or even from a fixating fluid which is 

 volatile (f.i. formaldehyde) into the soap. The method has been 

 described with much detail by M c. J u n k i n ; the great difficulty 

 is the choice of the right kind of soap. The author claims that 

 if one has once succeeded in finding a suitable kind, sections may 

 be cut thinner even than in paraffin. The soap is hardened 

 in a saturated salt-solution, before the sections can be cut; the 

 ribbon is dissolved away in water and the sections floated on 

 slides. This procedure takes a lot of practice, which is a 

 decided disadvantage of the whole method. 



In sections of the starfish radial sacs enormous quantities of 

 fat could be seen. The sections showed a typical greyish, almost 

 black color, which on closer examination appeared to be due 

 to numerous little fatdroplets in the epithelium. A similar obser- 



