45 



rally present in these infusoria, is built up from carbohydrates 

 or proteins. 



This example may illustrate the extreme difficulty of drawing 

 conclusions in problems of this kind. Biedermann in his 

 studies on the digestion of Helix and of the lar'va of Tenebrio, 

 is more definite in his statements. Yung already found that 

 fat can be emulsified by the contents of the gut of snails, 

 Biedermann and M o r i t z show that a steapsin is present. 

 This enzyme is more essential to their opinion. 



Milk to which the digestive fluid of these animals is added, 

 turns acid and coagulates. The residue, treated with osmic acid, 

 does not turn black. Fatty acids can actually be demonstrated 

 by ether extraction, addition of KOH or NaOH gives a turbid 

 solution or a jelly of the soaps. The free acids can be precipi- 

 tated from the solution by means of HCl (What about the 

 lactic acid which is known to occur in these digestive juices? 

 V. d. H. . — see the chapter on this topic — j. In the cells fat- 

 droplets can be seen „in zierlichen Reihen". 



„Man kommt so zu der Anschauung dass es sich bei der 

 Fettresorption nicht sowohl um eine Einlagerung von reinem 

 Fett in die betrefFenden Zellen, sondern vielmehr um eine Art 

 von Infiltration von neugebildetem Fett in eine andersartige 

 Grundsubstanz handelt, eine VorsteUung, die freilich mit der 

 herkommlichen einer direkten Au&iahme von genuinem, fein 

 verteiltem (emulgierten) Fett nicht wohl in Uebereinstimmung 

 zu bringen ist". 



These arguments sound rather convincing, the last word ho- 

 wever has not yet been spoken. I'll pass the numerous data 

 in the literature on the subject — ■ in nearly every order some 

 authors have reported the presence of emulsifying enzymes, 

 others that of a steapsin, while a third group denies its capacity 

 of digesting fats — , but first report on some experiments of my 

 own on Echinoderms. 



As a substrate I have used a neutral olive oil. I believe that 

 this substrate is very much better for the study of steatolytic 

 enzymes than commercial esters, like ethyl butyrate, which have 

 frequently been used for this purpose, because the latter sub- 

 strates only give us the right to draw conclusions about esterases, 

 not about a lipase. 



Fat is either taken up in hydrolysed form or as such. In 

 the latter case emulsifying enzymes must be present enabling 

 the cells of the wall of the gut to take hold of the smaU fat- 

 globules. 



For this reason it is in the first place necessary to make sure 

 whether such emulsification can be demonstrated. For this purpose 

 I secured samples of the intestinal juice of Asterias, Thyone 



