OBSERVATIONS ON STRIPED AND UNSTRIPED MUSCLE. 79 



network, or whether it is merely the false striation mentioned 

 above. 



Various modifications of the gold method were employed, according 

 to the delicacy of the tissue under investigation. The method 

 emploj'ed by Melland consists in placing the muscle in 1 per cent, 

 acetic acid for a few seconds ; then in 1 per cent, gold chloride for 

 thirty minutes • then in formic acid, 25 per cent., for twenty -four or 

 forty-eight hours in the dark. 



This answers well for vertebrate and insect muscles. But for the 

 more delicate organisms, such as Hydra, Daphnia, etc., and the 

 heart-muscle of invertebrates, I found a one hour's immersion in 

 formic acid, exposed to strong sunlight, to be the best treatment ; 

 or, in some cases, a warm chamber (40°C.) was used. A longer 

 immersion than one or two hours in the formic acid in these cases 

 leads to disintegration of the tissues. In addition to the gold pre- 

 parations, osmic acid preparations were made in most cases, and 

 compared with those made by the gold method. Osmic acid is well 

 known for its property of fixing the histological elements in their 

 natural state. 



The examination of fresh tissues was in many cases of very little 

 use ; for the cells of the striped muscle of many of the animals 

 investigated are so small that under a high power they barely appear 

 striped, and no network can be seen at all. In these cases it is only 

 by softening the fibre and so swelling it out, and at the same time 

 staining the network, that the latter can be demonstrated ; this is 

 the special action of the method of gold staining. 



It is necessary to mention that the results obtained by the gold 

 method are somewhat uncertain. In some cases the network will 

 come out distinctly, but in others, especially when the preparation 

 has been left for a longer time than usual in the acetic acid, the net- 

 work appears to consist of rows of granules instead of definite lines. 

 This uncertainty was noticed also by Kctzius, Gerlach, and Bremer, 

 and is no doubt the cause of the different appearances described by 

 these authors. 



In order to avoid the monotony and interruption of repeatedly 

 stating the treatment used for the muscle of each animal, the exact 

 method used is given with the description of the figure of each 

 animal in the plates at the end of the paper. 



