416 SUMMARY OF CURRENT RESEARCHES RELATING TO 



portant and more interesting forms. He supplies much information in 

 regard to economic importance, habits, and adaptations, and has suc- 

 ceeded in making his guide interesting as well as accurate. The book 

 is admirably illustrated. 



Mylostomid Dentition.* — C. R. Eastman discusses the dentition of 

 these Arthrodiran fishes, which are essentially like Dinkhthys, except 

 that their teeth are adapted for crushing instead of cutting. He deals 

 in particular with 31ijlostoma neivberryi sp. n. He concludes that all 

 known Dinichthyids, and at least one Mylostomid {31 ijlo stoma), have a 

 similar form of " premaxillary," which is the exact homologue of the 

 vomerine teeth in Dipnoans, and that the succeeding pair or pairs (when 

 two are present) of trenchant or crushing plates are homologous with 

 the palato-pterygoid dental plates of typical Dipneusti. The jaws 

 operate in the usual manner, are of the normal gill-arch type, and 

 exhibit precisely the same conformation as those belonging to autostylic 

 fishes. The combined evidence of the majority of characters of 

 Arthrodires proves that they are specialised Dipnoans. 



Rate of Tissue Disintegration.f — H. M. Vernon, to shed light ou 

 the chemical constitution of protoplasm, made a number of experiments 

 upon tissue disintegration in the kidney of the cat and the rabbit. The 

 fresh kidney was perfused for some days with saline solutions, and the 

 amounts of proteid, total nitrogen, and the ferment erepsin in the 

 perfused liquid estimated. From 27-GO p.c. of the tissue constituents 

 pass into solution. Addition of chloroform or ether to the perfusing 

 liquid greatly increases proteid and ferment disintegration. Already 

 perfused solution causes diminution of proteid and increase of ferment 

 disintegration. Change of salinity stimulates both. These reactions to 

 change of perfusing liquid are proportionate to the duration of perfusion 

 by the alternative liquid, and the effects produced are maximal at first 

 and gradually dwindle. The facts show that even dead tissue reacts 

 definitely to slight stimuli and exhibits some adaptation to environment, 

 making it seem possil)le that living protoplasm and dead protoplasm 

 differ in degree, not in kind. 



Conditions of Tissue Respiration.| — H. M. Yernon, by perfusion 

 experiments on the excised kidney of the rabbit and the cat, has shown 

 that the gaseous metabolism is at first as great as in the living animal, 

 but dwindles rapidly. The tissue contains about 100 c.cm. of intra- 

 molecular oxygen per kilogram. HCX hinders absorption of oxygen. 

 Perfusion with weak solutions of lactic acid, ammonia, sodium fluoride, 

 and arsenious acid causes diminution of gaseous metabohsm. Heating 

 the kidney to 55°-60°, and thus coagulating many of the proteid 

 constituents causes a decrease of gaseous metabolism, but does not 

 render it impossible. Loss of proteid from the kidney by disintegration 

 has httle effect on the tissue respiration. These last observations sup- 

 port Yerworn's hypothesis that respiration depends on non-nitrogenous 

 side chains in the biogen molecules. 



* Bull. Mus. Comp. Zool. Harvard, i. (1907) pp. 211-28 (1 pL). 

 t Zeitschr. allg. Phvsiol., vi. (1907) pp. 393-441. 

 t Jouru. of Physiol."', xxxv. (1906) pp. 53-87. 



