164 



Gust. Alsterberg 



d) On this transition of the normal rhythmical condition to dyspnoea, the 

 length commences to rise quickly, and, after its very last, greatest, and most 

 sudden ascent, it attains in the maximum dyspuœal stage its highest value, generally 

 at the same time as the frequency. This dyspuœal rise commences simultaneously 

 in all animals, and the reaction against maximum dyspnoea occurs when the 

 concentration of 0 2 is Oos c. c. per litre, or somewhat higher. 



e) From maximum dyspnoea, the length instantaneously sinks down to a 

 minimum, usually simultaneously with the frequency, without the animal totally 

 disappearing, however, into the mud. 



f) The length undergoes no further regular variations after this length-minimum 

 has been reached. The animal is in a state of asphyxia. 



g) According to what has already been adduced, the Tubifex responds, even 

 before maximum dyspnoea has begun, by migration, and does not therefore exhibit 

 the last stages of the length-reactions described in the foregoing, these reactions 

 applying to the Limnodrilus. 



h) If the variations of length are graphically represented by a curve with the 

 concentration of 0 2 as abscissa, this curve shows, still more clearly than the fre- 

 quency-curve, a strong rise to maximum dyspnoea, after which it instantly descends 

 to the asphyxiai minimum without subsequent change. The curve for apnosa- 

 eupncea-dyspncea is almost asymptotic in its form. 



3) By variations in the Displacement. On a sinking of the 0 2 tension, the 

 volume of the water displaced rises, as does the length and the frequency, in the 

 form almost of an asymptotic 'curve, with the low leg at the point where the 

 rhythm begins and the highest point at maximum dyspnoea. 



4) By variations in the absorption of nutrition, the animal ceasing to absorb 

 food when the 0 2 is at or under a certain low concentration (0'4 c. c. 0 2 per litre). 

 1 am disposed to interprète this reaction as an enterorespiratory dyspnoea, the respi- 

 ratory region increasing at the expense of the nutritive function. 



C. A particularly special case of varying percentage of 0 2 and peculiar 

 reactions responding to the variations in question, is denoted under experimental 

 conditions by diurnal periodicities in the animal's respiration, when green algae had 

 crept into the experiment. 



1) The diurnal periodicities were suspended under asphyxiai conditions. 



2) In sunlight, O a is generated, and to this the animals respond with maximum 

 dyspnoea. 



3) In bad light there is no generation of 0 2 , and the 0 2 previously present 

 is consumed by the mud and the animals, after which the latter respond as- 

 phyxially. 



4) The sharply pronounced nature of the diurnal periodicities is determined 

 by the discontinuous course between maximum dyspnoea and asphyxia. 



D. In the series of experiments in which I have proceeded from a lower 

 to a higher 0 2 percentage, by allowing the air to have free access to the surface 



