Microincineration of Active Smooth,Transitional and Skeletal Muscles. ∗

Abstract

The distribution of inorganic salts in the active and inactive smooth muscle of the intestine and the transitional muscle of the gizzard of birds and skeletal muscle is revealed by the technic of microincineration perfected by Scott. 1 He emphasized the distribution of ash in relatively inactive smooth and skeletal muscle by this method. He did not report in detail on the ash distribution in the active smooth, transitional, and skeletal muscles. This method of incinerating microscopic sections of tissue without disturbing the relationship of the mineral components was suggested by Liesegang 2 and developed by Policard. 3 The recent studies of Kruszynski 4 are on the topography of the mineral content in relatively resting muscle after microincineration.

The muscle is fixed for 24 hours in 9 parts of absolute alcohol and 1 part of neutral formalin. The mineral salts are neither increased nor decreased by this fixative. The tissue is completely dehydrated by several changes in absolute alcohol. The mineral salts remain intact by this method. It is then cleared in xylol, embedded in paraffin, and cut serially at 4 to 6 microns. Alternate sections are mounted by the usual method, and stained with hematoxylin and erythrosin, whereas, the intervening sections are mounted with liquid petrolatum to spread the tissue evenly. After the section is flat the excess liquid petrolatum is removed carefully by smooth blotting paper. The intervening sections are incinerated in a closed electric furnace at varying temperatures from 400° to 650°C.

The temperature is raised 50°C every 10 minutes until the highest temperature is reached. Sudden elevation of temperature with an excess of liquid petrolatum underlying the paraffin section results in explosive distortions due to sudden thermal agitation. The slide is cooled slowly over a period of 8 to 12 hours and the incinerated section is then covered with a number 0 cover glass around the edges of which melted paraffin is applied.