55 



11. Irritability of 3fuscles. — Dr. Todd* shows that the difference 

 in the excitability of muscles, in paralyzed parts, is due to the dif- 

 ferent state of the nervous force in the nerves of the paralyzed limbs. 

 In one class it is in a minus, in the other in a plus condition, and in 

 a third, is unaffected by the central lesion. Dr. Marshall Hall 

 ascribes an increase of irritability to the muscles of a paralyzed 

 limb. 



12. Contractions of Muscles. — M. Prevostf states that "When a 

 muscular fibril contracts, the folds lie close by the approach of the 

 particles which constitute the fibrinous cylinders; these gravitating, 

 as it were, in a longitudinal direction, occupy a less space, and thus 

 determine the appearance of folds." 



13. Muscularity of Arteries. — The muscularity of small arteries 

 has been proved by experiments with galvanism, made by E. & E. 

 H. Weber. J They show that arteries from J^ to 4 of a line in 

 diameter, were contracted to ^ their diameter, and, if the galvanism 

 was continued, thus diminished only a single row of blood-corpuscles 

 could pass through. 



14. Development of Muscle. — M. Prevost§ thus describes the de- 

 velopment of muscle: — "In the embryo of vertebrata the muscles of 

 animal life have primarily the form of gelatinous cylinders, very 

 transparent. Later the central part of these cylinders is organized 

 in reddish filaments. These occupy, little by little, all the interior 

 of the cylinders, and the jelly which surrounds them gradually thins, 

 and becomes a fine envelop. In vertebrata, Crustacea and insecta, 

 the muscles of animal life differ much from those of organic life ; 

 whilst the fibre of the heart holds a middle place. Muscles of volun- 

 tary movement present regular cylinders, but those of the intestines 

 consist of packets of straight juxtaposed fibres. In mollusca, the 

 movements of which remind us of peristaltic action, both systems 

 present fibres like those called organic." 



15. Development of the Heart. — MM. Prevost and Lebert an- 

 nounce the following remarkable discoveries in the early history of 

 the formation of the heart. In the chick there is a primitive heart, 



* Med. Gaz., July 25th, 1847. 

 X Miiller's Archives, No. 2, 1847. 



t Comptes Rendus, 31 Mai, 1847. 

 § Comptes Rendus, 22 Fevrier, 1847 



