QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 187 



narrow and sharply defined one. This Merkel explains as 

 the median disc, now exposed to view, in consequence of the 

 contractile substance having moved to either end of the 

 muscle compartment, where by its accumulation it causes the 

 apparent thickening of the terminal discs. Each muscle com- 

 partment, then, now contains a portion of solid contractile 

 substance at each end, in close connection Avith the terminal 

 disks, and a middle zone occupied by liquid and divided by 

 the median disc. Merkel was, after much trouble, able to 

 trace these changes while the process of contraction was 

 going on. The solution of the difficulty was given by cer- 

 tain fibres of the claws of cray-fish, plunged, when quite 

 fresh, in absolute alcohol. In them were seen some quite 

 homogeneous parts, on one side of which the fibre Avas in 

 the state of contraction, on the other side in a state of rest ; 

 and this intermediate homogeneous portion represents the 

 transitional stage between the two. (This Merkel believes 

 to be the true explanation of the perfectly homogeneous 

 fibres often described.) When the key had thus been found, 

 it was possible to trace successively the three stages of rest, 

 transition, and contraction in living fibres also. With regard 

 to the optical properties of muscle, Merkel asserts that, in 

 his " transitional stage," the whole fibril is doubly refracting, 

 and its optical effect shows that it is solid. In fact, there 

 must be at this moment, through the whole of the muscle 

 compartment, an intimate mixture of its solid..and fluid con- 

 tents. The area of each muscle compartment remains, 

 during contraction, precisely the same, as was shown by 

 direct measurement. 



"Muscles of the Small Bronchi and of the Lung Paren- 

 chyma."— Kindfleisch (' Centralblatt,' No. 5, 1872, p. 65) 

 gives the following preliminary communication on this 

 subject. The smallest bronchi have a very clearly marked 

 layer of transverse muscular fibres, which is strengthened so 

 as to form a comj)lete sphincter at the point where the 

 bronchus passes into the infundibulum. They are sus- 

 ceptible of considerable dilatation, and are furnished just 

 under the epithelium with a very close network of capillary 

 vessels, like those of the lung. (2) The circular muscular 

 bundles of the smallest bronchi send loop-like prolongations 

 into the opening of the infundibula, which penetrate to their 

 extremity. At a few points bands of smooth muscles form 

 rings round the infundibula. These muscular rings lie in 

 those parts of the alveolar septa wliich project most inwards. 

 (3) All these muscles are hyperplastic in the morbid con- 

 dition known as brown induration of the lunsr. When once 



