280 Dr Lazarus-Barloiu, A new method [April 29, 



Many varieties of miscible fluids of different specific gravities 

 were thought of and tried, for it is only necessary to have two 

 fluids on either side of the extremes of the specific gravity of the 

 tissues in order to be able by mixing them in different proportions 

 to obtain a series of fluids of known specific gravities, but since 

 these different fluids acted injuriously on the tissues themselves, 

 it is unnecessary to mention them. The material to be used was 

 indicated to me in reading a paper by Heffter^ in which he speaks 

 of gum-arabic as being a suitable nutrient fluid for experimental 

 work on the heart-muscle. He says that the amount of work the 

 frog's heart can perform when fed with a solution of gum-arabic 

 is greater than that which it can perform with many apparently 

 more nearly physiological nutrient media, such as solutions of egg- 

 albumen, &c. It follows therefore that we have here a material 

 which dissolved in water can be made up into solutions of different 

 specific gravity and which moreover will do as little damage as 

 possible to the fresh tissue immersed in them. Further, though 

 water certainly diffuses into gum solutions it diffuses with great 

 slowness so that it was probable that the specific gravity of the 

 tissue might be obtained before a sufficient amount of water had 

 been abstracted to lead to any considerable modification of the 

 initial specific gravity. 



Solutions of gum-arabic in water were therefore made of 

 specific gravity (as estimated by standard hydrometers) varying 

 from 1050 to 1080, viz, those most usually required. Alternate 

 fluids were coloured with a minute quantity of solid methylene 

 blue. The fluids were placed in bottles similar to the ordinary 

 "wash" bottle and the cork was covered with paraffin. A crystal 

 of thymol was placed in each bottle to prevent growth of micro- 

 organisms. Fluids have been kept in this way without modifica- 

 tion in specific gravity for over a year. When an estimation was 

 required the fluids were carefully placed in order in a large test- 

 tube, the fluid having the highest specific gravity being placed 

 first and the others above it in their order. There was thus 

 obtained a column of fluid consisting of sharply-defined blue and 

 yellowish bands each of which corresponded to a different specific 

 gravity. The piece of tissue being now removed from the body 

 and rapidly cleaned from blood, &c. on filter paper a portion is 

 placed gently in the uppermost fluid, care being taken to avoid 

 the entanglement of bubbles of air. It sinks rapidly through 

 the upper layers but more slowly as it reaches those layers with 

 which its own specific gravity more nearly corresponds until in 

 some one layer or more commonly at the line of junction between 

 two layers it obviously finds some obstacle to its further descent 



1 Heffter, Ueber die Ernahrung des arbeitenden Froschherzens, Arch. f. exp. 

 Path. u. Pharm., 1892, Vol. xxix, p, 50, 



