Volume 40, Issue 5
November 1954, pages 125-160
pp 125-137 November 1954
A new technique is described to determine the action of substances on the contractile mechanism of unstriated muscle. It consists in killing the muscle by heating it to 50° C. for a few minutes.
The results obtained on heat killed muscle are more or less similar to those on dying muscle with minor differences.
Active relaxation occurs if the muscle is heated to 50–60° C. As heat denatures the proteins, it appears that the process of relaxation of muscle is similar to that of denaturation of proteins. Most substances that denature proteins, cause unstriated muscle to relax actively. These experiments therefore throw light both on the process of relaxation and on that of denaturation of proteins.
Urea, sodium cyanide, distilled water, formamide, acetamide, acids and alkalies cause active relaxation of heat killed muscle.
Potassium chloride has similar action on heat killed muscle as on dying muscle. It causes two or three kinds of contraction. One of these is antagonised by calcium, and probably corresponds to superprecipitation of actomyosin. The other contractions are probably due to some other proteins.
The effect of sodium chloride resembles that of potassium chloride.
Possible mechanisms of tonus are discussed.
pp 138-144 November 1954
The neurosecretory system of the adult Chætodacus Cucurbitæ (Trypetidæ: Diptera) consists of the cerebral, thoracic and abdominal centres of secretory neurons.
The cerebral neurosecretory centres consist of the median and lateral neurosecretory cells of the pars intercerebralis. The cells show characteristic tintorial properties when stained in chrome-hæmatoxylinphloxin and in Azan, recalling the nature of similar cells in other insects.
The axons of the median cerebral neurosecretory cells are fairly long, and the nervi corporis cardiaci and corpus cardiacum show granules similar to those observed in the cytoplasm and axons of the cells.
The thoracic ganglion shows a more conspicuous set of neuro-secretory cells. They consist of an anterior, lateral anterior, lateral posterior and posterior cell clusters, which in the first three are paired.
The single abdominal ganglion contains a few neurosecretory cells also showing characteristic tintorial properties.
The nerve emerging from the abdominal ganglion and going to the gut shows blue granules traceable from the neurosecretory cells at the posterior end of the ganglion.
Phase contrast observations of the cells show that the neurosecretory cells of the fly have a general structure with prominent cytoplasmic products in the form of dark granules and large and small spheroids and globules.
Measurements of the thoracic neurosecretory cells, which forms the larger cells of the system, have been given.
pp 145-160 November 1954