104 CARNEGIE INSTITUTION OF WASHINGTON. 



combine physiological obseivations in developing animals with subse- 

 quent morphological examination of the same material, and in this 

 way to make definite progress towards the solution of some of the 

 fundamental problems of the central nervous system. Two papers 

 have been pubhshed concerning the reactions following decerebration. 

 It was found that decerebrate kittens do not exhibit an invariable 

 extensor rigidity such as is found in decerebrated adult animals. 

 They give, however, typical scratch reflexes, respond to both dorsal 

 and ventral excitation, and react to trauma to the tail. In general, 

 the animals after decerebration are much more active than are the 

 customary adult preparations. A point of particular interest is that 

 practically all of them show rhythmic progressive movements, and it is 

 possible to separate them into two groups on the basis of this reaction, 

 the groups being determined by the length of time the beats continue. 

 The reactions of the group which show prolonged progressive beats are 

 those of an adult cat, from which only the cerebral hemispheres have been 

 removed. The animals of the second group, however, are somewhat 

 more active than are adult decerebrate cats. In the kittens of the first 

 group an extensor rigidity was usually absent. Where it was not 

 absent a questionable rigidity occurred soon after the ablation, and was 

 quickly abolished by the onset of rhythmic beats of all four legs. As 

 the tendency to progression decreased extensor rigidity became more 

 pronounced, affecting in some only the forelegs. A reciprocal relation- 

 ship between the prolonged progressive movements and the extensor 

 rigidities seems to be indicated by these experiments. 



Dr. Weed has also pubhshed a paper regarding the anatomical 

 aspects and the more general processes of the circulation and distribu- 

 tion of the cerebro-spinal fluid, in which is reviewed the history of our 

 knowledge of the pathways of this fluid. He incorporates the results 

 of his own investigations, an account of which was given in my last 

 report. 



H. G. Fisher and H. R. Muller have reported their observations upon 

 cats experimentally subjected to unilateral destruction of the semi- 

 circular canals. Their particular purpose was to determine the per- 

 manency of the functional disturbances produced by such a lesion 

 and the amount of compensation which occurs on the part of other 

 organs. They find that such animals tend to slowly recover from the 

 initial disturbances in their postural and muscular reactions, but that 

 the recovery does not become complete, the longest observations 

 having extended over a period of three months. The characteristic 

 rotation when walking, when dropping through the air, or when sub- 

 merged in water, occurs always in the same direction — around the long 

 axis of the body and away from the lesion. 



During the year an investigation has been completed by Professor 

 George L. Streeter on the histogenesis of the mesodermal tissues sur- 



