THE PROCESSES OF LIFE IN PLANTS AND ANIMALS. 251 
it breathes, that is to say, the presence of oxygen is necessary for 
its life. Recapitulating these points it will be seen that the chief 
properties and functions of protoplasm are : — tst, contractility ; 
2nd, power of response to a stimulus, or irritability ; 3rd, recep- 
tion and assimilation; 4th, respiration. An important pheno- 
menon connected with the movements of protoplasm, and the 
one which forms the chief subject of this lecture, is its mani- 
festation of natural electric currents. If a fresh muscle of, say 
a frog’s hind leg, be taken and connected with the two poles 
of a galvanometer, it is found that there is a continuous current 
of electricity passing longitudinally through it. During the con- 
traction the natural muscle current is weakened or undergoes a 
negative variation. In nerves the effect is precisely similar, but 
the natural current is not so strong. During the passage of a 
nervous impulse along a nerve the natural nerve current under- 
goes a negative variation, just as in the case with a muscle in 
action. The same phenomena occur in sensitive plants. There 
is a natural current in the leaf of the dionea which undergoes a 
negative variation when the leaf is stimulated to contract by irrita- 
tion of one of its sensitive hairs. But the latent period inter- 
vening between the moment of stimulation and the beginning of 
contraction is longer in the vegetable protoplasm than in the 
animal muscle. Similar electrical changes are produced when the 
stigma of Mimulus luteus is stimulated to contract. The conclusion 
of the lecture was devoted to an exposition of some recent 
researches into the functions of the green colouring matter of 
plants. The most important facts as pointed out were :—That 
until late years it was supposed that chlorophyll was the part of 
plant which performed the digestive function. It is now known, 
however, that chlorophyll has no power to decompose carbonic 
acid. The chlorophyll when dissolved out of plants and examined 
by the spectroscope is found to absorb all the violet rays of the 
spectrum. The chlorophyll acts as a screen cutting off those rays 
which promote the decomposition of protoplasm. ‘The lecturer 
explained how hemoglobin when dissolved out of the blood acts 
precisely as blood does becoming black in carbonic acid, and 
scarlet in oxygen. 
The Chairman said he had heard Mr. Carpenter many times, 
but he had never listened to him with deeper interest. 
Mr. Harris asked if any experiments had been made as to the 
condition of the movements in the stamens of the Berberidz, and 
the leaves and petioles of the sensitive Mimosa ? 
Mr. Carpenter replied that he was not aware of any such 
experiments having been made yet, but that the subject was com- 
paratively a new one, and also presented very considerable technical 
difficulties. 
