It is well known that at a lower degree of mental development the power of instantaneous muscular exertion is far less than among educated men. Broca’s experiments showed that artisans with somewhat trained intelligence generally reached higher figures on a dynamometer than working men who were only used to bodily exertions. And the Negroes, whose forces were tested by Féré, were far below the average of Europeans.[393] As in these experiments the natives were introduced to new and unaccustomed movements, the evidence of the psychometric apparatus must be considered as somewhat extenuated by the circumstances. Broadly speaking, these experiments can, however, be taken as indications of a general psychological law.[394] The experimental evidence is, moreover, corroborated by the common complaints of Europeans who have had to rely on natives. The slowness with which the primitive man gets into swing with his work has no doubt been referred to times without number by slavekeepers when advocating their methods of treating natives. Strange to say, there are some tribes which themselves candidly admit their own inertness, and voluntarily submit to whipping in order to get “their blood a little agitated.”[395] The slowness and the insensibility of the Guarani are, however, as appears from Mr. Rengger’s description, exceptional and pathological.[396] But it seems as if almost all tribes had invented some means of inciting themselves to work. Only, these means are seldom such as Europeans would feel inclined to avail themselves of when urging on their workers. That they can nevertheless be as effectual as even the slavekeepers whip is shown by Signor Salvado. His description of his experiences with Australian natives as farm-labourers is delightful: “How often,” says he, “have I not used their dancing songs in order to encourage and urge them on in their work. I have seen them, not once, but a thousand times lying on the ground with minds and bodies wearied by their labour; yet as soon as they heard me singing the Machielò-Machielé, which is one of their commonest and favourite dancing songs, they would yield to an irresistible impulse, and rise and join me with their voices. They would even begin to dance joyfully and contentedly, especially when they saw me singing and dancing among them, like any other savage. After a few minutes of dancing I would seize the opportunity to cry out to them in a merry voice, Mingo! Mingo! a word meaning breast, which is also used in the same way as our word courage. After such an exhortation they would gradually set to work again. And they would begin afresh with such goodwill and eagerness, that it seemed as if the dance of Machielò had communicated to them new courage and new vigour.”[397]