362 Messrs. C. M. Tidy and W. B. Woodman on Ammonia [May 30, 



themselves in the "fry" of the osseous fish, their absence does not affect 

 the general skeletal morphology. 



The salmon amongst fishes, like the fowl amongst birds, never attains to 

 the greatest degree of special class-modification ; it remains subtypical, 

 with a dentigerous maxillary, a ductus pneumaticus, a very chondrosteus 

 state of the skull, and a very heterocercal tail. 



Yet, from an ichthyological point of view, this fish is an immense height 

 above the Sharks and Rays, and is far in advance, as a fish, of the whole 

 group of " Ganoids." 



The results of the gradational study of the fish-forms by the zoologist, 

 and of their secular study by the palaeontologist, are both in harmony with 

 morphological facts. Although the light obtained is but as the first streak 

 of dawn, yet it is a pleasant light, and quite sufficient to show each kind of 

 worker where and how to renew his own special toil. 



I cannot close this brief abstract without remarking that my researches 

 in these, the highest types of animals, seem to me to be in perfect accord- 

 ance with the results obtained by long study of the very lowest, the 

 Rhizopods — namely, that they both yield increasing evidence in favour 

 of the doctrine of Evolution. 



Researches of this kind show what the life-processes can accomplish in 

 the history of one individual animal, and also that the morphological steps 

 and stages are not arbitrary, but take place in a maimer in accordance with 

 all that has of late been revealed to us of the gradation of types in the ages 

 that are past. 



The following communications were read : — 



I. (< On Ammonia in the Urine in Health and Disease." By C. 

 Meymott Tidy, M.B., Joint Lecturer on Chemistry and Medical 

 Jurisprudence at the London Hospital ; and W, Bathurst 

 Woodman, M.D., Joint Lecturer on Physiology, and Assistant 

 Physician to the London Hospital. Communicated byT. Blizard 

 Curling, President of the Royal Medical and Chirurgical Society. 

 Received April 16, 1872. 



(Abstract.) 



The authors refer to the researches of Andrews, Clark, Xeubauer and 

 Yogel, and others on the presence of ammonia as a constant constituent 

 of healthy urine, Xeubauer regarding 10*8 grains per diem as the average 

 normal excretion. After numerous experiments, the authors regard this 

 quantity as excessive, and suggest some reasons for this discrepancy. 



The method adopted by the authors is as follows :— 



The freshly passed urine is to be first diluted with a given bulk of dis- 

 tilled water, sufficient to destroy all apparent colour, a known quantity 

 of the urine being taken in each case. To these is to be added an excess 



